A standard easy-open package comprises a vessel having a flat rim and a profiled or planar cover foil that is bonded to the vessel along an annular seal strip at the rim, the vessel and the foil being made of a synthetic resin, a metal, or a laminate of the two materials. The vessel and foil together form one or more compartments that can contain respective foodstuffs, although it is within the scope of this invention for other types of materials to be thus packaged. As a rule the foil and vessel are bonded together, either by a weld or an adhesive, along the rim, that is the outer periphery of the vessel. The bond is made weak enough that the foil can be removed without tearing yet strong enough to keep the contents hermetically contained. This clearly creates for the manufacturer the problem of trading off ease of opening against sealing. Another problem is that it is possible for different materials, typically foodstuffs, to slip from one compartment to another between the top of a rib or web separating one compartment from the adjacent one.
It is also known to form the cover foil with a tear line that extends around the compartments, just within the inner edge of its periphery and with an open or lift tab attached to the foil within the tear line. The tab is pulled up away from the vessel to strip that portion of the cover foil that lies inside the tear line from the package. Such an arrangement is fairly difficult to make, in particular when the vessel is to have several compartments.